In generally, a contact-detecting device includes a reference electrode and a working electrode immersed into a solution and electrically connected to the electric meter to form a circuit. The reference and working electrodes interact chemically with ions in the solution to generate a potential difference (potentiometric sensor) or an electrical current difference (amperometric sensor) in the circuit, and the electric meter measures the potential difference or the electrical current difference to detect the ion concentration.
The reference electrode is usually a silver/silver chloride (Ag/AgCl) electrode coated with a polymeric membrane having ionized material, like ionized chloride material. When the reference electrode is immersed in a test solution, the polymeric membrane and the test solution exchange the ions, and then exchange the ions with the Ag/AgCl electrode, like that, the polymeric membrane protects the Ag/AgCl electrode and the process provides a stable and fixed reference potential. The working electrode is coated with a sensing membrane, and the sensing membrane detects the ion concentration of the test solution to generate an electric current, and the electric current intensity represents the ion concentration. A different ion concentration generates a different current, that is, to measure the current to obtain the ion concentration.
USPTO issued a patent (U.S. Pat. No. 6,932,894), referred to FIG. 1, using a polymeric membrane 20 having cross-linking polymer of heterocyclic nitrogen to detect the glucose concentration. The polymeric membrane 20 covers a working electrode 14, a reference electrode 16 and a sensing layer 18. A substrate 12 separates the working electrode 14 and the reference electrode 16, and the sensing layer 18 is on the working electrode 14. The device has a high stability, high efficiency and a wider sensing range, but the device is only suitable to the glucose concentration and not suitable to the ion concentration.
The traditional ion solution concentration-detecting device with separating reference electrode and the working electrode is not convenient, and the integrated device, like U.S. Pat. No. 6,932,894, is not suitable to the various ion concentrations. There still needs to improve the convenience and efficiency of the ion solution concentration-detecting device.